Even though some users of the two desktops take every opportunity to make fun or flat-out attack one another, it is no secret to more reasonable people that the KDE and GNOME projects strive to make their respective desktops interoperate, and that the developers working on either of the two projects have a great deal of respect for one another. This has lead to an attempt to jointly organise the desktops' flagship conferences, in one place, in 2009.

Gah! 'Choice is Free Software / Open Source's greatest strength. 'World Domination' is a call to rally developers, not good policy at the high level. The level of 'sameness' between the big projects has been pretty much where it needs to be. That is to say:

-GCC ABI compatibility is there so binaries are somewhat portable between distros and versions.
-The LSB is there to define a 'base environment'.
-Freedesktop.org is hosting a lot of 'glue specs' and 'glue technologies' that help the big desktops play nice with each other to varying degrees.

Beyond that, you don't want to encourage a monoculture. Competition tends to make the competitors better in the Free Software and Open Source world. It motivates developers, and it lets them steal each other's ideas.

Nothing illustrates this better than GNOME vs KDE. GNOME wouldn't exist if it wasn't for the initial Qt licence. GNOME freed Qt. Thanks GNOME. Gnome then competed with KDE to try to close the feature gap. Even with big distro support they were kind of relegated to 'a clunkier less mature KDE' sort of status. So then people envisioned GNOME 2... Which was a radical departure, but existed in roughly the same space as KDE. As GNOME 2 found it's 'sexy' it encouraged KDE, in the KDE 3 days, to begin cleaning up its config screens and interfaces. GNOME 2 continues it's march. It forces KDE to take a good look at itself and ask hard questions about what KDE is, should be, and most importantly isn't. The KDE camp comes up with a solid plan for KDE 4. Abstracted away from the OS, sexy, with clean(er) interfaces, sane defaults, and better organized config screens. They didn't 'neuter' the features-- but they raised the bar away from 'it might be cool if' features and 'some dude requested' features' as they tended to be the big bitrotting bug generators. And sure enough, now there's all of this talk from the GNOME camp about breaking BC, and a new cycle of GNOME innovation.

Now, if you were to ask either the GNOME or KDE camp if the 'other' was the primary motivator, they'd probably say “no”... But the push me / pull me is there. And every user is better for it. It forces evolution and prevents stagnation. Real change in the Free Software world comes from a projects 'peers' (Both withing a project and from other projects) not it 'less free rivals'.

Shouting down the GNOME / KDE /XFCE people for not merging with the other camp is actually harmful and stifling. Besides, most Free Software and Open Source developers are still volunteers, and you only diminish the pool of developers that way. The same goes for shouting down a new project that exists in the same space as an established project. The world might not need another text editor, but I'm happy that Compiz encouraged KDE 4's kwin to 'bring the bling' in a well integrated KDE sort of way...

I think this joint conference exists in the finest tradition of the Free Software 'competitive peer' system. Good for them!